Sealing means for liquid cooled rotors for dynamoelectric machines

ABSTRACT

Gland seals are provided for the entrance and discharge passages of liquid cooled rotors for dynamoelectric machines. Coolant liquid is introduced or discharged through stationary coolant chambers surrounding the rotor and enclosing the entrance and discharge passages. Gland seal rings encircle the rotor adjacent the coolant chambers and sealing liquid is introduced into the clearance between each seal ring and the rotor at a pressure not exceeding the pressure of the coolant liquid to minimize leakage of the coolant liquid while preventing contamination of the coolant liquid by the sealing liquid.

11/1969 Heard ..310/58 9 United States Patent 1111 3,733,501 -Heller etal. [4 1 May 15, 1973 541 SEALING MEANS FOR LIQUID 3,626,717 12 1971Lorch .310/54 COOLED ROTORS FOR 3,353,043 11/1967 Albright 3,393,3337/1968 Kudlacik DYNAMOELECTRIC MACHINES 3,145,314 8/1964 Becker [75]Inventors: Paul R. Heller, Murrysville, Pa.; 3,457,440 7/1969 Horsley..310/52 Ram T. Gehani, Bombay, India Primary Examiner-R. Skudy [73Assgnee' ga gfljgg a Cmmmn Attorney-A. T. Stratton and F. P. Lyle [22]Filed: Sept. 17, 1971 [57] ABSTRACT [21] Appl. No.: 181,479 Gland sealsare provided for the entrance and discharge passages of liquid cooledrotors for dynamoelectric machines. Coolant liquid is introduced (g1"310/2162? or discharged through stationary coolant chambers [58] Fieid58 56 surrounding the rotor and enclosing the entrance and 310/59discharge passages. Gland seal rings encircle the rotor adjacent thecoolant chambers and sealing liquid is in- [56] References Citedtroduced into the clearance between each seal ring and the rotor at apressure not exceeding the pressure UNITED STATES PATENTS of the coolantliquid to minimize leakage of the coolant liquid while preventingcontamination of the coo- 10/1970 Lang "310/58 lant liquid y the i g q i12 Claims, 3 Drawing Figures PATENTEDHAYI 5198 3133.50 1

SHEET 1 UF 2 PATENTEBHAYI 5l975 SHEET 2 OF 2 FIG. 2

FIG.

BACKGROUND OF THE INVENTION The present invention relates to liquidcooled rotors for dynamoelectric machines of large size, such as turbinegenerators, and more particularly to sealing means for the passages oropenings through which coolant liquid is introduced into and dischargedfrom the rotor.

Large turbine generators are usually of the inner cooled, or directcooled, construction in which a coolant fluid is circulated through ductmeans in the stator and rotor slots in direct thermal relation with thecurrent-carrying conductors inside'the ground insulation. This type ofconstruction provides a very effective cooling system and has made itpossible to greatly increase the maxirnum ratings obtainable in largegenerators without exceeding the permissible limits of physical size.The coolant used in these machines has usually been hydrogen, whichfills the gas-tight housing and is circulated by a blower on the rotorshaft through the ducts of the stator and rotor windings and throughducts in the stator core. 4

The maximum ratings required in large generators have continued toincrease, however, making it necessary to further improve the cooling ofthese machines in the largest sizes. A substantial improvement incooling can be obtained by the use of more efficient coolant fluids suchas liquids. This has been done in stators by circulating a liquidcoolant such as water through the ducts of the stator winding, and aconsiderable improvement in cooling has thus been obtained. Asubstantial further improvement can be obtained by applying liquidcooling to the rotor by circulation of a suitable liquid such as waterthrough passages in the rotor windings.

Many problems are involved, however, in circulating a liquid coolantthrough passages in the rotor of a large generator rotating at highspeed, usually 3,600 rpm. One of the most difficult problems is that ofintroducing the liquid into the rotor and discharging it therefrom. Theliquid is preferably introduced along the axis of the shaft, where thecentrifugal force on the liquid is at a minimum, and is dischargedthrough radial passages in the rotor shaft. A relatively large volume ofliquid must be introduced into the rotor under sufficient pressure tomaintain the desired flow rate through the rotor, and the same liquid isdischarged from the rotor at high velocity and under high pressure intoa stationary discharge chamber from which it is drained. Suitable sealsmust be provided at both the entrance and discharge openings orpassages, but the provision of such seals presents a difficult problembecause of the high velocities and pressures involved. The necessity ofeffective seals for this type of rotor cooling has been recognized inthe prior art, as in the patents to Fechheimer US. Pat. No. 2,527,878and Heard et al. US. Pat. No. 3,398,304, for example, but nosatisfactory seal has actually been'available heretofore.

The known types of seals for rotating shafts all have seriousdisadvantages for the present purpose. Labyrinth seals are well knownbut such seals are not effective for such coolant liquids as waterbecause of the large clearances required and the low viscosity of water,which result in excessive leakage through the seal. Friction or facetype seals are also well known. These seals, however, are impracticalfor large, liquid cooled turbine generator rotors because of the veryhigh rubbing velocities which may, for example, be in excess of 20,000feet per minute. Such velocities result in very rapid wear withexcessive heating and friction loss. Fluid film gland seals usingstationary seal rings are more suitable for the difficult conditions ofservice under consideration. The known single flow type ofcircumferential ring seal, however, would have excessive leakage ofliquid through the annular clearance because of the high pressure dropacross the ring. The

coolant must be treated to decontaminate the water and to remove excessoxygen to minimize possible corrosion. The leakage and subsequent lossof large amounts of this treated water is undesirable as it would meanthat a large amount of treated makeup water would have to be provided,requiring an increased amount of expensive treating equipment andincreased cost of treatment. Leakage of the treated coolant musttherefore be minimized.

SUMMARY OF THE INVENTION In accordance with the present invention, aliquid cooled rotor for large turbine generators is provided withveryeffective sealing means at both the entrance and discharge passages forpreventing escape of the coolant liquid. The seals are of the radialgland seal type utilizing a stationary sealing ring encircling the shaftadjacent a stationary coolant chamber which contains the coolant liquidentering or discharged from the shaft. The seal ring encircles the shaftwith a small clearance and in order to minimize leakage of the coolantliquid through the clearance, a secondary or sealing liquid isintroduced into the clearance between the ring and the shaft and ismaintained at a pressure not exceeding the pressure in the coolantchamber. A small amount of the coolant liquid may therefore escapethrough the clearance around the shaft, but the amount of liquidescaping is minimized and any contamination of the coolant liquid by thesealing liquid is prevented. The sealing liquid, together with a smallamount of coolant liquid, escapes into a chamber adjacent the seal ringwhich is maintained at atmospheric pressure and is drained therefrom.This chamber is sealed to prevent the escape of liquid along the shaft,and an adjacent chamber containing air at a pressure above atmosphericis provided to prevent liquid from escaping from the atmosphericchamber. In this way, a very effective sealis provided even for largevolumes of liquid at high velocities and pressures.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 3 is a similar view of thesealing means at the discharge passages of the rotor.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1 of thedrawings, the invention is shown embodied in a large turbine generatorof typical construction, although it will be understood that the sealingmeans of the present invention may be used in machines of anydesiredtype.

As shown, the generator has a stator core supported by frame rings 12 ina substantially gas-tight outer housing 14. The stator core 10 is of theusual laminated construction having a generally cylindrical boretherethrough, and the laminations are clamped between suitable endplates 15 in the usual manner. The stator core 10 has longitudinal slotsin its inner periphery for the reception of a stator winding 16 whichmay be of any suitable type but which is shown as a liquid cooledwinding. For this purpose circular inlet and discharge manifolds 17 areprovided at opposite ends of the machine and connected through suitablemeans, generally indicated at 18, to circulate a coolant liquid such aswater through the coils of the stator winding 16. The manifolds 17 maybe connected as indicated diagrammatically at 19 to an externalrecirculating system of any desired type. The housing 14 is filled witha coolant gas, preferably hydrogen, which is circulated through theinterior of the housing to cool the stator core, and suitable bafflingof any desired type may be provided in the housing to direct the flow ofgas therein.

The machine has a rotor member 20 which is disposed in the bore of thestator core 10 and supported in bearings 21 in the ends of the housing14. The bearing assemblies preferably include gland seals to preventleakage of gas along the rotor shaft and may be of any suitable or usualconstruction but have not been illustrated in detail as they are not apart of the invention. The rotor member 20 has a central body portion 25which is provided with the usual peripheral slots for the reception of arotor winding 26. The winding 26, which constitutes the field winding ofthe generator, may be arranged in any suitable manner in the slots ofthe rotor to form the desired number of magnetic poles, usually eithertwo or four in machines of this type. The winding 26 is constituted ofcopper conductors which extend longitudinally through the slots of therotor body 25 and generally circumferentially in the end turn portions28, which lie beyond the ends of the body portion 25 and which aresupported against rotational forces by the usual heavy retaining rings29. The conductors of the rotor winding are hollow, or have centralpassages extending through them, for flow of coolant liquid from one endof the winding to the other. Any suitable or desired type of flowpattern may be utilized and any desired type of electrical circuit maybe used.

The rotor 20 shown in the drawing is a liquid cooled rotor of theconstruction more fully disclosed and claimed in a copending applicationof L. P. Curtis et al., Ser. No. 144,050, filed May 17, 1971, andassigned to the assignee of the present invention. The rotor 20 hasshaft portions 30 extending axially from each end of the body portion 25and preferably integral therewith, and has a central axial bore 31 whichin accordance with usual practice may extend for the entire length ofthe rotor from one end to the other. An exciter 32 is provided forsupplying field excitation to the winding 26. The exciter 32 may be ofany desired type and has a shaft connected to the shaft 30 of the rotorto be driven therewith and which is, in effect, a part of the rotorshaft. As more fully described in the above-mentioned copendingapplication, the coolant liquid which is preferably water is introducedthrough the shaft of the exciter 32 into the shaft portion 30 at theleft end of the rotor, as seen in FIGJI. For this purpose, the excitershaft includes a central tube or pipe 33, preferably of stainless steelor other corrosion resistant material, which is coaxial with the rotorshaft and which extends outwardly from the exciter shaft, as shown inthe drawing, for the introduction of water.

The water flows through the tube 33 along the axis of the exciter shaftand is directed into an annular passage 34 in the bore 31 of the rotor20. The passage 34 is preferably formed by two concentric stainlesssteel tubes which surround axial electrical leads 35 which provideelectrical connection from the exciter 32 to the rotor winding 26. Thewater flows through the passage 34 to opposed radial passages 36 whichextend to an annular distribution chamber 37 on the surface of the rotorshaft 30. Water is distributed from the annular chamber 37 by means ofhydraulic connectors 38 of any suitable type to the individualconductors of the rotor winding, the connections being made to the endturns 28. The water flows through the hollow conductors of the rotorwinding to the other end and is discharged through similar hydraulicconnectors 39 to an annular collecting chamber 40 on the shaft 30 at theright-hand end of the rotor. The water flows from the chamber 40 throughtwo opposed radial passages 41 to the bore 31 of the shaft, and axiallythrough the bore 31 to opposed radial passages 42 which extend to thesurface of the rotor shaft 30.

All the passages and surfaces exposed to the liquid are preferably linedor covered with stainless steel or other corrosion resistant material toprevent corrosion of the rotor steel by the heated coolant water. Inparticular, the bore 31 at the right-hand end of the rotor is lined witha tubular stainless steel liner 43 extending between the two sets ofradial passages 41 and 42, and the ends of the liner are closed bysuitable plugs or partitions 44 to close this section of the bore 31 andconfine the coolant liquid thereto.

The coolant water is thus introduced into the rotor through the rotatingtube 33 which is on the axis of the exciter shaft, and is dischargedfrom the rotor through the radial passages 42. As previously explained,it is necessary to provide very effective seals at these points toprevent escape of the coolant water which flows through the rotor inrelatively large volume and at high velocity and pressure.

At the entrance end, as shown in detail in FIG. 2, water is suppliedthrough a stationary pipe or conduit 45. The pipe 45 is connected to astationary seal housing 46 which surrounds the end of the rotatingentrance tube 33, and the pipe 45 is connected to the housing 46 in anysuitable manner to form a leak-proof joint. The flanged end of the pipe45 and theseal housing 46 form a coolant chamber 47 surrounding andenclosing the open end of the rotating entrance tube 33. The coolantwater which has been suitably treated is supplied through the pipe 45under the necessary pressure to maintain the required flow of liquidthrough the rotor and fills the chamber 47 from which it flows into thetube 33. The sealing means contained in the housing 46 prevents escapeof water from the chamber 47 on the outside of the tube 33. The seal isof the radial gland seal type and includes a seal ring 48 contained inan an nular chamber 49 surrounding the tube 33. The ring 48 encirclesthe tube 33 with a small radial clearance, which may be of the order ofa few mils, and fits in the chamber 49 with as small a clearance aspossible to minimize leakage past the ring in the radial direction. Theseal ring 48 is stationary in the chamber 49 and may be held againstrotation in any desired manner. Another annular chamber 50 surrounds thetube 33 adjacent the chamber 49 and is maintained at atmosphericpressure in any suitable manner.

It will be apparent that since the liquid in the coolant chamber 47 isat relatively high pressure, the pressure drop across the clearancebetween the ring 48 and the tube 33 is correspondingly high, and theleakage of coolant water through this clearance into the chamber 50would be quite large. This is undesirable because the coolant water istreated to maintain a high level of purity and to remove dissolvedoxygen and is recirculated after discharge from the rotor. The loss of asubstantial amount of this liquid is therefore undesirable as it wouldrequire an increased capacity of treating and pumping equipment tosupply the necessary large amounts of treated makeup water. In order tominimize the leakage of coolant or primary water through the seal ringclearance, the ring 48 has a plurality of radial openings 51 extendingthrough it and a supply of untreated sealing or secondary water isprovided through a pipe 52 into the chamber 49. The sealing liquid thusflows through the openings 51 into the clearance space between the ring48 and the tube 33. If the pressure of the sealing liquid suppliedthrough the pipe 52 could be kept exactly equal to the pressure in thecoolant chamber 47, there would obviously be no leakage of coolantliquid and the sealing or secondary liquid would fill the clearanceunder the ring 48 and escape into the chamber 50. Since it is notpossible, with actual pressure regulators, to continuously maintain thepressure of the sealing liquid exactly equal to that of the coolantliquid, suitable pressure regulating means are provided to maintain asmall pressure difference such that the pressure of the secondary orsealing liquid is less than that of the coolant liquid by a smallpredetermined amount, such as 0.25 psi, for example, or in any eventdoes not exceed the pressure of the coolant liquid. Thus, any leakage isof the coolant liquid into the sealing liquid, and the coolant liquidflowing into the tube 33 is not contaminated by untreated sealingliquid. Since the pressure of the sealing liquid is only slightly lessthan that of the coolant liquid, the amount of coolant liquid which canescape through the clearance under the seal ring 48 is extremely limitedand total leakage is very effectively minimized.

The sealing liquid, with a small amount of coolant liquid, escapesthrough the seal ring clearance into the chamber 50, which is maintainedat atmospheric pressure, and is drained from the chamber 50 through adrain pipe 53 (FIG. 1). A thrower 54 is preferably provided on the tube33 within the chamber 50 to remove any water flowing on the tube. Alabyrinth seal 55 is preferably provided between the outer wall of thechamber 50 and the tube 33 to seal the chamber 50. Since some water willtend to follow the shaft and get past the thrower 54, there is atendency for some leakage through the labyrinth seal 55. In order toprevent this, another annular chamber 56 is provided on the outside ofthe chamber 50, with a seal 57 between the outer wall of the chamber 56and the tube 33. The chamber 56 is maintained at an air pressuresomewhat above atmospheric, in any suitable manner, and this pressurizedchamber prevents leakage of water through the labyrinth seal 55. A finalannular chamber 58 may encircle the shaft adjacent the chamber 56 toprotect the seal 57 and to maintain the pressurization of the chamber56.

At the discharge end of the rotor, as shown in FIG. 3, the coolant waterwhich has passed through the rotor is discharged through the opposedradial passages 42 into a stationary discharge housing 60 whichencircles the shaft 30 and encloses the radial passages 42. As morefully described in another copending application of L. P. Curtis et al.,Ser. No. 182,368, filed Sept. 21, 1971 and assigned to the assignee ofthis invention, each of the radial passages 42 preferably has a closureplug 61 at its outer end with a suitable restricting orificetherethrough to control the flow of water discharged from the rotor. Thecoolant water thus discharged flows into the stationary coolant chamber62 which surrounds the shaft and the water in this chamber is drainedtherefrom through a suitable drain pipe 63 (FIG. 1). The coolant liquiddischarged in this way is preferably cooled and treated as previouslydescribed, or otherwise, and recirculated to the entrance supply pipe45, or it may be disposed of in any other desired manner.

The discharge and recirculation system for the coolant liquid maycontain means, such as a throttle valve, for restricting the flowsufficiently to keep the chamber 62 filled with water in order to avoidcavitation. In some cases, however, such as where the surface velocityof the rotor shaft is very high, it may be preferable to keep thechamber 62 drained and avoid contact of the water with the shaft as faras possible. It will be obvious that the chamber 62 can be operatedeither filled with water or drained, by suitable control of thedischarge flow. The pressure in the chamber 62 must of course be greaterthan atmospheric in order to permit the water to be discharged, but thepressure should preferably not be any higher than is necessary, so as tominimize leakage through the seals.

The chamber 62 is sealed on both sides by sealing means similar to theseal utilized at the entrance end and described above, and similarelements have been given the same reference numerals in FIG. 3. It willbe seen that on each side of the chamber 62 there is provided astationary seal ring 48 in an annular chamber 49. The secondary orsealing liquid is supplied through pipes 52 to the chambers 49 andescapes through the seal ring clearances to the chambers 50 atatmospheric pressure. The sealing liquid is supplied at a pressure notexceeding the pressure in the chamber 62, to prevent contamination ofthe coolant water as previously explained, and the sealing liquid with asmall amount of coolant water leakage escapes from the chambers 50through suitable drain pipes 64 (FIG. 1). The chambers 50 are sealed bylabyrinth seals 55 and pressurized air chambers 56 are provided toprevent leakage through the seals 55. The sealing means on each side ofthe chamber 62 are thus essentially identical to the entrance sealingmeans shown in FIG. 2 and described above, and operate in exactly thesame manner.

Sealing means have thus been provided which are very efl'ective incontaining, with minimum leakage, the

large volume of high pressure coolant water circulated through the rotorof a large generator. In both entrance and discharge seals, the coolantis contained in a chamber encircling the rotating shaft or tube and ismaintained at a relatively constant pressure in this chamber which ismade as low as possible consistent with the requirements for circulationof the liquid. Gland seal rings encircle the shaft or tube adjacent thecoolant chamber but such rings alone would not prevent excessive leakagebecause of the high pressure drop across the clearance between the ringsand shaft. In order to minimize this leakage, a secondary or sealingliquid is introduced through the rings into the clearance around theshaft and kept at a pressure not exceeding the pressure in the coolantchamber. Thus, leakage of coolant liquid is minimized, and the sealingliquid is prevented from contaminating the coolant liquid in the chambersince any leakage will be outward from the coolant chamber into thesealing liquid. A relatively large volume of sealing water will becirculated in this way, but since this water does not have to be treatedand can be directly recirculated from the drain pipes 53 or 64 to thesupply pipes 52 it is not objectionable. A very effective seal is thusprovided which substantially prevents escape of any significant amountof water at either entrance or discharge end of the rotor and thus veryeffectively minimizes the loss of treated coolant water.

A preferred embodiment of the invention has been shown and described forthe purpose of illustration but it will be apparent that othermodifications and embodiments of the invention are possible, and allsuch modifications are within the scope of the invention.

We claim as our invention:

1. In a dynamoelectric machine, a rotor member including shaft portionsand having passages for circulation of a liquid coolant therethrough,said passages including entrance and discharge passages in the shaftportions for introducing coolant into the rotor and discharging ittherefrom, sealing means associated with said entrance and dischargepassages, each of said sealing means comprising a stationary coolantchamber surrounding the shaft and containing coolant at a predeterminedpressure, said coolant chamber having a small clearance with the shaft,a stationary seal ring encircling the shaft with a small clearanceadjacent said coolant chamber, means for introducing a sealing liquidinto the clearance between said seal ring and the shaft, said sealingliquid being maintained at a pressure not exceeding the pressure of thecoolant liquid, a stationary chamber surrounding the shaft adjacent theseal ring for receiving liquid flowing between the ring and the shaft,means for sealing said last-mentioned chamber, and means for drainingliquid from the lastmentioned chamber.

2. The combination defined in claim 1 in which the last-mentionedchamber is maintained at atmospheric pressure and has labyrinth sealmeans between the chamber and the shaft.

3. The combination defined in claim 2 including another chambersurrounding the shaft adjacent the labyrinth seal means and containingair at greater than atmospheric pressure.

4. The combination defined in claim 1 in which said seal ring iscontained in an annular chamber adjacent the coolant chamber and hasradial openings therethrough, and means for applying sealing liquid tosaid 8 annular chamber to flow through said openings to the clearancebetween the seal ring and the shaft.

5. In a dynamoelectric machine, a rotor member having passages forcirculation of a liquid coolant therethrough, said rotor member havingshaft portions at each end thereof, said passages including an entrancepassage comprising an open tube extending coaxially from one of saidshaft portions and rotatable therewith, said passages further includingopposed radial discharge passages in one of said shaft portionscommunicating with an axial passage to discharge coolant therefrom,entrance seal means associated with said rotatable tube, discharge sealmearis associated with said discharge passages, each of said seal meansincluding a stationary coolant chamber surrounding the rotor member witha small clearance and containing coolant under pressure, a stationaryseal ring adjacent the coolant chamber and encircling the rotor memberwith a small clearance, means for introducing a sealing liquid into theclearance between the seal ring and rotor at a pressure not exceedingthe pressure of coolant in the coolant chamber, and means for containingand draining ofi sealing liquid flowing between the seal ring and therotor.

6. The combination defined in claim 5 in which each seal means includesan annular chamber adjacent the seal ring for receiving sealing liquid,said annular chamber being sealed and maintained at substantiallyatmospheric pressure, and means for draining sealing liquid from theannular chamber.

7. The combination defined in claim 5 in which said entrance seal meanscomprises a stationary coolant chamber enclosing the open end of saidrotatable tube and containing coolant under pressure, a stationaryannular chamber adjacent said coolant chamber containing said seal ring,means for introducing sealing liquid through said annular chamber to theseal ring at a pressure not exceeding the pressure of the coolant, asecond annular chamber adjacent the seal ring for receiving sealingliquid, said second annular chamber being maintained at a pressure belowthe pressure of the sealing liquid, means for sealing the second annularchamber, and means for draining sealing liquid therefrom.

8. The combination defined in claim 7 including a labyrinth seal betweenthe second annular chamber and the rotor, and another chamber adjacentthe labyrinth seal containing air at a higher pressure than the pressurein the second annular chamber.

9. The combination defined in claim 5 in which said discharge seal meanscomprises a stationary coolant chamber enclosing said dischargepassages, said coolant chamber containing coolant under pressuredischarged from said passages and having means for draining coolanttherefrom, a stationary seal ring encircling the shaft on each side ofthe coolant chamber, stationary annular chambers adjacent the coolantchamber on each side thereof and containing the seal rings, means forintroducing sealing liquid through said annular chambers to the sealrings at a pressure not exceeding the pressure in the coolant chamber,other annular chambers surrounding the shaft adjacent each of said sealrings for receiving sealing liquid, each of said other chambers beingmaintained at a pressure below the pressure of the sealing liquid, meansfor sealing said other chambers, and means for draining sealing liquidtherefrom.

10. The combination defined in claim 9 including a labyrinth sealbetween each of said other chambers and the shaft, and a chamberadjacent each labyrinth seal containing air at a higher pressure thanthe pressure in said other chambers.

l l. A shaft seal for preventing escape of liquid along a rotatingshaft, said seal comprising a stationary chamber through which the shaftpasses, said chamber containing liquid under pressure, a stationary sealring encircling the shaft with a small clearance adjacent said chamber,means for introducing a flow of sealing liquid through said clearancebetween the seal ring and the shaft, the pressure of the sealing liquidnot exceeding the pressure of the liquid in said chamber, a stationarythe pressure in the annular chamber.

1. In a dynamoelectric machine, a rotor member including shaft portionsand having passages for circulation of a liquid coolant therethrough,said passages including entrance and discharge passages in the shaftportions for introducing coolant into the rotor and discharging itTherefrom, sealing means associated with said entrance and dischargepassages, each of said sealing means comprising a stationary coolantchamber surrounding the shaft and containing coolant at a predeterminedpressure, said coolant chamber having a small clearance with the shaft,a stationary seal ring encircling the shaft with a small clearanceadjacent said coolant chamber, means for introducing a sealing liquidinto the clearance between said seal ring and the shaft, said sealingliquid being maintained at a pressure not exceeding the pressure of thecoolant liquid, a stationary chamber surrounding the shaft adjacent theseal ring for receiving liquid flowing between the ring and the shaft,means for sealing said last-mentioned chamber, and means for drainingliquid from the last-mentioned chamber.
 2. The combination defined inclaim 1 in which the last-mentioned chamber is maintained at atmosphericpressure and has labyrinth seal means between the chamber and the shaft.3. The combination defined in claim 2 including another chambersurrounding the shaft adjacent the labyrinth seal means and containingair at greater than atmospheric pressure.
 4. The combination defined inclaim 1 in which said seal ring is contained in an annular chamberadjacent the coolant chamber and has radial openings therethrough, andmeans for applying sealing liquid to said annular chamber to flowthrough said openings to the clearance between the seal ring and theshaft.
 5. In a dynamoelectric machine, a rotor member having passagesfor circulation of a liquid coolant therethrough, said rotor memberhaving shaft portions at each end thereof, said passages including anentrance passage comprising an open tube extending coaxially from one ofsaid shaft portions and rotatable therewith, said passages furtherincluding opposed radial discharge passages in one of said shaftportions communicating with an axial passage to discharge coolanttherefrom, entrance seal means associated with said rotatable tube,discharge seal means associated with said discharge passages, each ofsaid seal means including a stationary coolant chamber surrounding therotor member with a small clearance and containing coolant underpressure, a stationary seal ring adjacent the coolant chamber andencircling the rotor member with a small clearance, means forintroducing a sealing liquid into the clearance between the seal ringand rotor at a pressure not exceeding the pressure of coolant in thecoolant chamber, and means for containing and draining off sealingliquid flowing between the seal ring and the rotor.
 6. The combinationdefined in claim 5 in which each seal means includes an annular chamberadjacent the seal ring for receiving sealing liquid, said annularchamber being sealed and maintained at substantially atmosphericpressure, and means for draining sealing liquid from the annularchamber.
 7. The combination defined in claim 5 in which said entranceseal means comprises a stationary coolant chamber enclosing the open endof said rotatable tube and containing coolant under pressure, astationary annular chamber adjacent said coolant chamber containing saidseal ring, means for introducing sealing liquid through said annularchamber to the seal ring at a pressure not exceeding the pressure of thecoolant, a second annular chamber adjacent the seal ring for receivingsealing liquid, said second annular chamber being maintained at apressure below the pressure of the sealing liquid, means for sealing thesecond annular chamber, and means for draining sealing liquid therefrom.8. The combination defined in claim 7 including a labyrinth seal betweenthe second annular chamber and the rotor, and another chamber adjacentthe labyrinth seal containing air at a higher pressure than the pressurein the second annular chamber.
 9. The combination defined in claim 5 inwhich said discharge seal means comprises a stationary coolant chamberenclosing said discharge passages, said coolant chamber containingcoolAnt under pressure discharged from said passages and having meansfor draining coolant therefrom, a stationary seal ring encircling theshaft on each side of the coolant chamber, stationary annular chambersadjacent the coolant chamber on each side thereof and containing theseal rings, means for introducing sealing liquid through said annularchambers to the seal rings at a pressure not exceeding the pressure inthe coolant chamber, other annular chambers surrounding the shaftadjacent each of said seal rings for receiving sealing liquid, each ofsaid other chambers being maintained at a pressure below the pressure ofthe sealing liquid, means for sealing said other chambers, and means fordraining sealing liquid therefrom.
 10. The combination defined in claim9 including a labyrinth seal between each of said other chambers and theshaft, and a chamber adjacent each labyrinth seal containing air at ahigher pressure than the pressure in said other chambers.
 11. A shaftseal for preventing escape of liquid along a rotating shaft, said sealcomprising a stationary chamber through which the shaft passes, saidchamber containing liquid under pressure, a stationary seal ringencircling the shaft with a small clearance adjacent said chamber, meansfor introducing a flow of sealing liquid through said clearance betweenthe seal ring and the shaft, the pressure of the sealing liquid notexceeding the pressure of the liquid in said chamber, a stationaryannular chamber surrounding the shaft adjacent the seal ring forreceiving said sealing liquid, said annular chamber being maintained ata pressure below the pressure of the sealing liquid, means for sealingthe annular chamber, and means for draining liquid therefrom.
 12. Ashaft seal as defined in claim 11 in which the means for sealing theannular chamber includes a labyrinth seal between the chamber and theshaft and another chamber encircling the shaft adjacent the labyrinthseal and containing air at a pressure higher than the pressure in theannular chamber.